Medical personnel, including dentists and physicians, often inject an anesthetic into a patient prior to performing various procedures, such as drilling cavities, preparing teeth for crowns and tooth extractions, to name a few.
FIGS. 1A-C illustrate a prior art anesthetic carpule 110 (FIG. 1A), a pre-injection dental syringe 150 (FIG. 1B) and corresponding syringe needle 160 (FIG. 1B) and a post-injection dental syringe 150 (FIG. 1C). As shown in FIG. 1A, a carpule 110 has a glass or plastic tube 112 having a first end 101 and an opposite second end 102. A rubber stopper 114 seals the first end 101 and a diaphragm 115 held in place by an aluminum cap 116 seals the second end 102. An anesthetic 118 is contained in the tube 112 between the sealed ends 101, 102. An aperture 117 in the cap 116 allows needle access to the anesthetic 118 via a punctured hole in the diaphragm 115.
As shown in FIG. 1B, the carpule 110 is loaded into a syringe 150 for injection. A needle 160 is inserted through the diaphragm 115 and held in place with a needle cap 162 pressed over a threaded syringe port 153. A plunger 154 engages the rubber stopper 114 via a harpoon 152 piercing the exposed end of the stopper. The plunger 154 is used to eject any air from the needle prior to insertion of the needle 162 into a patient tissue site. The harpoon 152 allows the plunger to slightly withdraw the stopper so as to aspirate the syringe, insuring the needle is not in a blood vessel. As shown in FIG. 1C, after aspiration, the plunger drives the rubber stopper down the carpule, injecting the carpule contents into the tissue site.